The Human Immunodeficency Virus has caused a worldwide pandemic. Supporting strategies through basic science research that treat and prevent infectious disease like HIV is part of NIAID's mission. The purpose of this work is to elucidate the virus-host cell interactions mediating virus release in HIV-infected cells. In HIV-1 infected T cells, virions bud from the plasma membrane. However, in HIV-1 infected macrophages virions bud into multivesicular bodies. What accounts for this difference in budding phenotype? This study will examine how interactions between HIV-1 Viral Protein U, a host protein Twik-associated Acid Sensitive K+ channel-1(TASK-1), and other TASK-1 interacting cellular proteins, in HIV-infected cells affect HIV release;the goal of this study is to determine whether or not these interactions account for the cell type dependent differences observed with regard to virus release. Specific Aim 1: To determine the consequence of the TASK-1-Vpu interaction with respect to TASK-1 localization and function in HIV-infected macrophages and T cells. This aim will focus on assessing TASK-1 expression, localization, and activity in both primary T cells and macrophages. TASK-1 expression, localization, and activity will be examined and compared upon infecting each cell type with wild-type HIV, a naturally occurring HIV-1 isolate harboring a vpu deletion mutation or a vpu expression plasmid. Specific Aim 2: To determine the function of specific TASK-1-binding cellular proteins and TASK-1 activators with respect to the differential pattern of virus release in HIV-infected T cells and macrophages. In macrophages, HIV budding occurs through the exocytic pathway [2]. TASK-1 binds to 14-3-3 and annexin II, two proteins that have been shown to regulate TASK-1's intracellular localization. These TASK binding proteins both participate in exocytosis. Annexin II also binds directly to HIV-1 Gag, a structural protein that localizes to sites of virus assembly and release during HIV infection. TASK-1 may function as adaptor protein that bridges viral and cellular factors together in order to promote virus release. To address this hypothesis, annexin II, and 14-3-3 expression and localization, in primary T cells and macrophages, will be examined before and after HIV-infection. These findings will be correlated with TASK-1 expression and localization in the same cells. The site of virus assembly and release will be identified using transmission electron microscopy in cells expressing wild-type TASK-1 and TASK-1 mutants, wherein the binding sites for annexin II or 14-3-3 have been disrupted. The goal of this proposal is the better understand how HIV manipulated host cell machinery in different cells types for HIV egression. Understanding these pathways will help us to design ways to block HIV release and decrease the burden of infection.